v0.4.3

• No longer keep fits files open unless we are actually reading them.
• Expose MWA coordinates as library constants.
• Added the reading of FREQCENT key from the metafits file to mwalibContext.
• Allow passing no gpubox files (i.e. mwalib will read only the metafits file) when creating an mwalibContext instance.
• Read digital gains and dipole delays from metafits. (Currently unavailable via FFI).
• Specify Rfinput polarisation as an enum instead of a string.
• For full list, see CHANGELOG.md